Transdermal systems constitute a form of medication for a patient, wherein an active ingredient, mostly provided on a plaster or patch, is absorbed for some time (often for several hours or days) through the patient's skin in the underlying vessels or the underlying tissue.
This form of medication makes it possible to bypass the first-pass metabolism, i.e. the first liver passage. This can reduce the required dosage of active ingredient. This helps to prevent overdosage that is stressful for organs and circulation.
A known transdermal therapeutic system is offered by “passive” patches, for instance fentanyl patches for tumor pain therapy or nicotine patches for enabling people to stop smoking. These “passive” patches are left on the skin for some time, e.g. up to 72 hours, thereby continuously releasing their active ingredient from an adhesive layer. The patch is then replaced.
Although the active ingredient can thereby be released through the skin continuously for some time, this release process cannot be actively controlled during application on the skin.
It is however advantageous to release the active ingredient in dosed form for a specific period of time because this will then permit an individual medication for the patient. Thus a controllable transdermal therapeutic system makes it possible to minimize the total amount of active ingredient released with the same therapeutic efficiency.
Such a controllable system is represented by electrochemically operating transdermal therapeutic systems in which the active ingredient is stored in an adhesive layer. With the help of two electrodes an electric field is applied to the adhesive layer. Owing to the action of the electric field applied the active ingredient is delivered in dosed form.
In this electrochemically operating release method, however, the respective active-ingredient molecule must carry a corresponding charge. Moreover, the delivered dose is predetermined by the value of the potential difference and by the duration of the electric field applied.
Moreover, all of the transdermal therapeutic systems that have so far been available are based on an immobilization of an active ingredient in an adhesive layer, which frequently causes contact allergies in the patients concerned, i.e. independently of the active ingredient itself.